Researchers in physics education have repeatedly shown that traditionally taught introductory courses have minimal effect on the conceptual understanding, problem solving skills, and scientific reasoning ability of most students' including physics majors. Much of that research suggests that lingering difficulties can adversely impact student learning of more advanced material. Research in the context of sophomore/junior level courses in intermediate mechanics has been particularly fruitful in investigating student learning beyond the introductory level. Such research has also been invaluable in guiding the development and assessment of innovative instructional strategies that can complement (and exceed the effectiveness of) traditional lectures. This presentation will highlight results from research conducted at Grand Valley State University, the University of Maine (by co-PI Michael Wittmann) and pilot site institutions in the Intermediate Mechanics Tutorials project. We present evidence of specific student difficulties as well as examples of the use of guided inquiry in addressing these difficulties.